1. Field of the Invention
The present invention relates to a self-heating container capable of heating liquid food such as Japanese sake, liquor, coffee or milk, water, oil or the like contained therein.
2. Description of the Prior Art
There has been well known in the art a method for heating or warming liquid contained in a container by using a heating element or exothermic material. In general, food or the like is heated by utilizing hydration of calcium oxide (burnt lime), oxidation or burning or combustion of metal powder.
For instance, Japanese Utility Model Application Laid-Open Nos. 60-70235 and 60-94130 disclose a method in which a chamber for receiving therein exothermic material is defined within a container. Calcium oxide and a water bag are provided in the chamber. When the water bag is broken, an exothermic reaction is started to heat the content in the container. In this method, however, a ratio of a volume of the exothermic material storage chamber to a volume of a content storage space of the container is high, so that its thermal efficiency is not satisfactory. When it is desired to heat the content in the container sufficiently, there arise problems that a large-sized container is required and that a space not filled with the content is likely to be heated. More particularly, when liquid food or the like is charged into the container and then the container is sealed, a space not filled with liquid is generally left. Therefore, depending upon an attitude of the container, such a space is heated by the activated exothermic material, so that the pressure in the container rises to result in explosion thereof.
The same problems arise also in the case of a self-heating container of the type disclosed in European Patent Application Laid-open No. 0180375. In this container, a portion for storing calcium oxide and a water bag is defined around the outer wall of a container to be heated, so that its thermal efficiency is further degraded. Furthermore, there is a danger of burn when the outer wall of the exothermic material storage portion is not sufficiently thermally insulated.
In the above-described inventions, calcium oxide (burnt lime) is used as exothermic material, so that there arise problems that it takes a long time to heat the content to a desired temperature and that after heating the content, calcium oxide expands, resulting in deformation of the container.
U.S. Pat. No. 4,506,654 for Zellweger et al. discloses a heating device in which a container is heated by a combustible exothermic material flatly mounted on the bottom of the container. Japanese Utility Model Application Laid-Open No. 57-55772 discloses a self-heating container of the type in which exothermic material which undergoes an exothermic reaction in the case of its oxidation with oxygen in the air is stored in a concave recess at the bottom.
The self-heating containers of the types described above, however, have a common defect that a space in the container not filled with liquid is overheated when the container is turned upside-down or inclined horizontally or diagonally. In addition, the thermal efficiency is also low, because a part of high temperature heat is dissipated in the direction opposite to the content.
Furthermore, Japanese Patent Application Laid-Open No. 56-64971 discloses a container which is heated when water is added to exothermic material consisting of ammonium persulfate and manganese powder. Such a container, however, requires a large volume of an exothermic material storage portion, and accordingly the same problems as those in case of calcium oxide (burnt lime) are encountered.
Moreover, Japanese Patent Application Publication No. 27-582 or Japanese Utility Model Application Publication No. 58-24119 discloses a heating device in which exothermic material mainly consisting of trilead tetraoxide and ferrosilicon is filled in a metal cylinder. However, a heat output per unit of weight of such exothermic material is relatively low and furthermore there is the possibility that toxic compounds such as lead monoxide result after the combustible reaction, so that from a view point of safety, such exothermic material is not preferably used when heating food.
As described above, in a heating device utilizing exothermic material, the selection of a suitable exothermic material and a design of a container to be heated by the exothermic material are very closely related to each other and therefore most of the conventional heating devices have some defects.